problem in finding vth by vth0

[alireza sm]

in my hspice program all of Vbs in mosfet transistors are zero but in some mosfet transistors as seen in their operation points in file .lis vth is not equal to vth0 and has a value more than vth0. can anyone tell me why this happens?

 

[csolis_GT]

The latest models for transistors includes more factors than vbs when calculating the vth of a device. As an example, W and L will affect vth to some extent. I would say that typically the value quoted for the vtho is for minimum length lmin and wide width (maybe >10*wmin) like you would implement in digital circuits. You can experiment with different size combinations and see how vth changes.